This invention relates to a method of producing surfactants from lignin. More particularly, the invention discloses a process of alkylating, sulfonating and then oxidizing lignin to form a group of compounds having water soluble surfactant properties. These compounds may be used in surfactant flooding to recover hydrocarbons from underground formations.
Surface active compounds or surfactants have become extremely important chemicals in our society. Numberless types of surfactants are used for a myriad of applications. To work effectively, most surfactants require water soluble and oil soluble characteristics. It is these mixed characteristics which enable surfactants to lower the surface tension between two disparate liquids.
One problem with many surfactants is their high cost of manufacture. Surfactants which are relatively cheap have an inherent advantage in the marketplace.
A minor use of surfactants has been in surfactant flooding systems for enhanced oil recovery. But because of the relatively high cost of surfactants, surfactant flooding systems for oil recovery have generally not been economical.
Surfactant flooding to recover oil has been actively investigated due to the relatively poor ability of waterfloods to displace remaining oil from a reservoir's pore structure. Because of the reservoir structure and surface tensions involved, the floodwater may form channels or fingers, bypassing the oil in the formation.
Investigations of ways to increase oil recovery by improving the displacement ability of waterfloods have produced useful surfactants which reduce the interfacial tension between oil and water in the reservoir. With lower interfacial tensions, oil that is trapped in the pore structure can be dispersed into the water as smaller and more easily deformable droplets. Many types of surfactants have been investigated and the choice of which surfactant to employ in a waterflood operation is dependent upon reservoir characteristics as well as the cost and availability of the surfactants.
Lignin is a waste by-product that the pulping industry produces in prodigious amounts. As a result, a large research effort has been undertaken over the last 40 years in attempts to find uses for the large volume of lignin by-product.
Lignin is comprised of polymeric chains having molecular weights over 10,000 with multiple different units. One substantial monomeric unit contained in the lignin polymeric chains is propane phenol.
Numerous oxidation methods of lignin have been tried. The oxidation of lignin by potassium permanganate and sodium periodate is disclosed in Griggs, B. F., "Modification of Kraft Lignins by Sulfomethylation and Oxidative Sulfonation: Structure and Mechanisms", Ph.D. Dissertation, North Carolina State University (1985). The Griggs Dissertation isolated eight specific benzoic acid structures having single or double aromatic rings as oxidation products of lignin. Other potential oxidizing agents have been used to oxidize side chains on benzene. Potassium permanganate is disclosed in Whitmore, F. C. and Woodward, G. E., Organic Synthesis. Coll., Vol. I, p. 159 (I944). Chromic acid in aqueous solution is disclosed in Pacaud, R. A. and Allen, C. F. H., Organic Synthesis, Coll., Vol. 2, p. 336 (1943). Chromic acid in acetic acid as an oxidizing agent of side chains has been disclosed in Rieveschl, G., Jr., and Ray, F. E., Organic Synthesis. Coll., Vol. 3, p. 420 (I955). Aqueous sodium dichromate is another potential oxidizer of lignin side chains at elevated temperatures. See, Friedman, L. J. Organic Chemistry, Vol. 43, p. 80 (1963). Nitric acid has also been employed to oxidize lignins as disclosed in Popa, V. I., Cellulose Chem. Technology. Vol. 19, p. 657-661 (1985).
Mild oxidizing agents of lignin such as copper(II) oxide or sulfate, cobalt(II) oxide or sulfate and nitrobenzene are disclosed in Sarkanen, K. V. and Ludwig, C. H., "Oxidation," Chapter 11 of Lignins -Occurrence, Formation, Structure and Reactions, John Wiley & Sons, Inc. (1971); and Leopold, B., "Aromatic Keto- and Hydroxy-Polyethers as Lignin Models," Acta Chemica Scandinavica. Vol. 4, p. 1523-37 (1950).
Several literature references have discussed a procedure for identifying various structures within lignin polymers. This identification method involves methylating lignin at phenolic groups followed by oxidation with potassium permanganate or potassium permanganate followed by hydrogen peroxide. Please see, Freudenberg, K. and Chen, C. L., Chem. Ber., Vol. 93, p. 2533 (1963); Freudenberg, K., Chen, C. L. and Cardinale, G., Chem. Ber., Vol. 95(11), p. 284 (1962); and Griggs, B. F., Ph.D. Dissertation previously cited.
Procedures on how to make alkyl ethers from lignins may be found in Brauns, F. E., Lewis, H. F. and Brookbank, E. B., "Lignin Ethers and Esters," Industrial and Engineering Chemistry, Vol. 37(1) (1945); and Jones, G. M. and Brauns, F. E., "Ethers of Certain Lignin Derivatives," J. Paper Trade, Vol. 119(11), p. 108 (1944).
U.S. Pat. Nos. 4,739,041 and 4,790,382 describe a method of producing surfactants from lignin which comprises subjecting lignin to two reactions, alkylation and oxidation. The patent discloses similar results regardless of which reaction occurs first. The lignin surfactants are used in surfactant floods for enhanced oil recovery. However, when preparing surfactant systems with divalent ion brines, these lignin derivatives must be dissolved in fresh water followed by the addition of the other compounds and brine. They will not dissolve in divalent brines alone. They must first be solubilized in fresh water before adding other components. In many cases this is a drawback since fresh water is not readily available in large quantities in the field.
U.S. Pat. Nos. 4,739,040 and 4,787,454 disclose a method of surfactant flooding with lignin surfactants produced by reducing lignin in the presence of a carbon monoxide or hydrogen reducing agent at high temperature and pressure to produce low molecular weight lignin phenols, and subjecting the lignin phenols to one or a combination of several reactions such as alkoxylation, alkylation, sulfonation, sulfation, alkoxysulfation, and sulfomethylation.
Another lignin surfactant variation is disclosed in U.S. Pat. No. 4,781,251 wherein an alkylphenol lignin surfactant is employed in a surfactant flooding system. The alkylphenol lignin surfactant is produced by reacting an alkylphenol having about 6 to about 15 carbon atoms in the alkyl chain with formaldehyde in basic solution at an elevated temperature to form a first reaction product. The first reaction product is then reacted with a kraft lignin at elevated temperature to form an alkylphenol lignin reaction product. Finally, the alkylphenol lignin reaction product is made more water soluble by a reaction selected from the group consisting of sulfonation, sulfation, alkoxysulfonation, alkylsulfation and alkoxylation to produce the alkylphenol lignin surfactant.